Biochemical measurements of skin integrity were conducted to measure the skin s response to toxic chemicals, which included aqueous solutions of sodium fluoride or lead acetate, and xylene solution of benzo [a] pyrene as positive controls. Receptor fluid bathing the visceral side of excised pig skin was assays for lactate production as an indicator of the main energy- producing pathways, for the enzyme lactic acid dehydrogenase (LDH) as an indicator of cell lysis, for color changes in a redox dye to indicate alteration in the oxidation-reduction capacity of the tissue, for RNA nucleosides as an indicator of aberrant RNA metabolism, and for accumulation of mutagenic products. Alteration of pyrimidine nucleoside excretion by skin was the most sensitive indicator of exposure to chemical or biological insults. We propose that alterations in ribonucleosides from excised skin will serve as sensitive indicators of exposure to skin irritants. We further propose to conduct such tests using a novel diffusion cell array based on standard 24 well culture plates. PROPOSED COMMERCIAL APPLICATION Development of new materials that contact the skin (e.g. topical drugs, cosmetics) usually requires an assessment of skin irritation potential in an animal model. There is a demand in commerce for an in vitro test that would reduce animal usage and produce results more predictive for man. Development of our technology will provide such a test with significant advantages over currently available test kits.